Fuel cells are electrochemical energy conversion devices that have demonstrated a potential for relatively high efficiency and low pollution in power generation. A fuel cell generally provides a direct current (dc) which may be converted to alternating current (ac) via, for example, an inverter. The dc or ac voltage can be used to power motors, lights, communication equipment and any number of electrical devices and systems. Fuel cells may operate in stationary, semi-stationary, or portable applications. Certain fuel cells, such as SOFCs, may operate in large-scale power systems that provide electricity to satisfy industrial and municipal needs. Others may be useful for smaller portable applications such as, for example, powering cars.
A fuel cell produces electricity by electrochemically combining a fuel and an oxidant across an ionic conducting layer. This ionic conducting layer, also labeled the electrolyte of the fuel cell, may be a liquid or solid. Common types of fuel cells include phosphoric acid (PAFC), molten carbonate (MCFC), proton exchange membrane (PEMFC), and solid oxide (SOFC), all generally named after their electrolytes. In practice, fuel cells are typically amassed in electrical series in an assembly of fuel cells to produce power at useful voltages or currents.
In general, components of a fuel cell include the electrolyte and two electrodes. The reactions that produce electricity generally take place at the electrodes where a catalyst is typically disposed to speed the reactions. The electrodes may be constructed as channels, porous layers, and the like, to increase the surface area for the chemical reactions to occur. The electrolyte carries electrically charged particles from one electrode to the other and is otherwise substantially impermeable to both fuel and oxidant.
Typically, the fuel cell converts hydrogen (fuel) and oxygen (oxidant) into water (byproduct) to produce electricity. The byproduct water may exit the fuel cell as steam in high-temperature operations. This discharged steam (and other hot exhaust components) may be utilized in turbines and other applications to generate additional electricity or power, providing increased efficiency of power generation. If air is employed as the oxidant, the nitrogen in the air is substantially inert and typically passes through the fuel cell. Hydrogen fuel may be provided via local reforming (e.g., on-site steam reforming) or remote reforming of carbon-based feedstocks, such as reforming of the more readily available natural gas and other hydrocarbon fuels and feedstocks. Examples of hydrocarbon fuels include, but are not limited to, natural gas, methane, ethane, propane, methanol, and other hydrocarbons.
Fuel cell systems include many components to transfer heat between streams of fuel, to transfer heat between streams of air, and to oxidized the discharged effluent from the fuel cells. These components typically are separate and spatially distributed apart from each other. A significant amount of conduits (e.g., in terms of the number of conduits and/or the total length of the conduits) may be needed to fluidly couple these components. As the amount of conduits needed increases, the amount of heat loss from the fuel and/or air flowing through the conduits increases. As a result, the conduits may need to be fabricated from more thermally insulative (and, therefore, more expensive) materials and/or additional heating components may need to be added to the system. This increases the cost and complexity of the fuel cell systems.